texts: Why is true and average anomaly of planet important?

texts: Why is a true and average anomaly of the planet important? What useful information do they give us?


texts: What caused instant jumps and exactly flat periods in Kepler's light curves?

texts:
Last 65 days of Kepler's light curve for the infamous KIC 8462852 star is shown below from the published paper's graph. Skip the dips here, I wonder about two other features:

Day 1559, during a period which is calm but also the very brightest, the light curve instantly and permanently drops by half of a percent.
Days 1581 to 1587 the light curve is exactly flat (also days 803-809
not shown here). Is the real data for those periods lost?

Are such features commonplace or another particularity for KIC 8462852?

How wide would a confidence interval typically be for a finished Kepler light curve when all adjustments for telescope movements and whatnot have been made?


texts: How can I observe the Orionid Meteor Shower?

texts:
I would like to see the orionids sometime this week (October 20-26, 2013). What is the best way for me to observe them by naked eye?

Also, would I be benefitted by trying to look at them with a telescope or or are they too fast and spontaneous for most amateurs to capture?


texts: "Juxtapositions" of moon,stars and planets in the sky,

texts: What are "Juxtapositions" of the Moon, stars and planets called? When the Moon, stars and planets take exactly the same position after few or many years, how to describe the positions and what is called to describe the position?


texts:
The latest big quasar find at ~12.8 bn LJ with an estimated mass of 12 bn M☉ (see e.g. http://www.newscientist.com/article/mg22530104.000-ancient-black-hole-had-an-inexplicable-growth-spurt.html) puts current black-hole-forming hypotheses into question. As the linked article explains, scientist doubt that most of the matter could pass into the hole in such a short time due to the outward pushing force of the radiation created by the material falling into it.

My question is rather, was there enough matter in such a close vicinity of a BH that it could grow to this size? At 900 million years from the big bang I have the feeling that there is hardly enough time for the required matter to even pass through the volume around the BH where accretion can happen.


texts:
The solar system is thought to have a heliopause which can be considered its edge for many purposes:

The heliopause is the theoretical boundary where the Sun's solar wind is stopped by the interstellar medium; where the solar wind's strength is no longer great enough to push back the stellar winds of the surrounding stars. This is the boundary where the interstellar medium and solar wind pressures balance.

  Heliopause: the boundary between solar wind and interstellar wind where they are in equilibrium.

Is there a similar phenomenon at the interface between space dominated by the Milky Way and intergalactic space?

What is at the edge of the Milky Way galaxy?


texts:
I'd like to determine the distance at which a telescope with a certain set of parameters (sensitivity, collector area) can detect a blackbody with certain other parameters (temperature, emitting area).

For example, let us suppose we have an infrared telescope with a sensitivity of '1Jy/sr' and a collector area of 10m^2 at a distance D from a 300m^2 perfectly black body at a temperature of 30 Kelvin.

How do I determine D? What additional information do I need to perform the calculation?


texts: What is the shape of the Sun's orbit around the Earth taking into account elliptical orbits?

texts:
Consider the non-inertial frame that is at rest with respect to the Earth's revolution around the Sun.  (Ignore the Earth's rotation around its own axis.)  My question is, what is the shape of the Sun's orbit around the Earth in this reference frame?

Now if we assume the Earth moves in a circular orbit around the Sun, then the Sun's orbit around the Earth will also be circular. (Just use geometric the definition of a circle - the set of all points a fixed distance from a given point.). Specifically it's the great circle formed by the intersection of the ecliptic plane with the celestial sphere.

But the Earth does not move in a circular orbit - Kepler's first law states that the Earth moves in an ellipse around the Sun, with the Sun at one of the foci of the ellipse.  So if we consider the Earth's elliptical orbit around the Sun, what is the shape of the Sun's orbit around the Earth.  I doubt it's an ellipse, so would be it a more complicated-looking curve.

Note that I'm not interested in gravitational influences from the moon and other planets - this is pretty much a purely mathematical question: if we assume the Earth moves in an ellipse, what would be the shape produced?


texts: how far away could we detect that Earth has life?

texts:
My guess is that life bearing planets are too far apart to be detected. I think we can only find the ones within a sphere around our planet that is 100s of light years in diameter but I suspect life bearing planets may be much farther away than that.

I would like to estimate the diameter of the sphere within which we could detect life on another planet and then estimate the probability that there is life within that sphere.

For example, give our current technology what is the furthest distance would be able to detect life on Earth?
How many stars like our sun are in that sphere?
How long would it take for SETI to rule out each of those stars?


texts: Do some ELF (Extremely low frequency) radio waves pass the atmosphere

texts: ...reach Earth surface and then are reflected passing the atmosphere again to reach outer space? And once in outer space can they travel indefinetely in it or the interplabetary plasma would stop them? This occurs only when when the plasma is excited? When it is not, these radio waves would be able to make it through?


texts: River-like artifact in perseverance rover's photo of Mars

texts:
Good to know that perseverance rover has touched the surface of Mars finally. We will have nice new opportunity window for exploring our closest "friendly" planet of solar system.
Here's one of Mars photos perseverance has made :

Question is, What are this object roots marked with rose color ? I suspect it can be remains of past river in Mars or is it just an artifact of wind+sierra effect ?


texts: Do Astronomers really never call Lagrangian points "libration points"?

texts:
In this answer to Who called the Lagrangian points as “Libration” points and and why was the terminology “Libration” used? I described my feeling that Lagrangian points were also sometimes called "libration points" because for the the linearized equations of motion in the circular restricted three body problem at least some of these were equilibrium points where a small displacement would result in oscillatory motion and some of these are called halo orbits and Lissajous orbits. We know some of these are unstable even in CR3BP but for a few periods at least they are oscillatory.
Then I wrote:
Interestingly former NASA engineer, flight director and Space Shuttle program manager, Wayne Hale's October 2019 blog post Definition of Terms covers this very question, and seems to disagree with this viewpoint!
I recommend reading the full post for sure, but to summarize the post shows some "libration points" of the Moon, where lunar libration is maximum.

The spot on the edge of the moon that is tilted the most toward an earthly observer is called ‘the libration point’.
Have you heard that term before?  I bet you have but in a different context.
Joseph-Louis Lagrange (1736-1813) was an Italian mathematician who played a large part in the development of the metric measurement system (SI) in post-revolutionary France.  He also studied orbital mechanics involving three bodies (e.g. sun/earth/moon) and mathematically proved there are locations around such an orbit which are gravitationally stable.  These points are called Lagrange points in his honor.  There are typically 5 such points and I will leave it to the student to research their locations.
As you can see Lagrange points and Libration points are quite different and literally have nothing to do with each other.
But if you read any number of popular media stories – and even several NASA technical papers – there appears to be confusion and the terms are used interchangeably.  This is so widespread that some dictionaries have started changing the definitions to keep up with what appears to be popular usage.
STOP THAT!
Unfortunately, the curmudgeon in me realizes that this erroneous usage has become so common that it will be hard to change usage in popular literature.
But at least you now know the difference.  And you, like me, will stop when you hear some ‘expert’ (never an astronomer) mixes the terms and think about how much ignorance is being displayed.

Question: Do astronomers really never refer to any Lagrangian points as "libration points" as Wayne Hale's blogpost asserts?


texts: Is there any url that can give me  data of ecliptic line that i can plot in a map. i.e i need earth's latitude and earth's longitude of ecliptic line for a specific time and date. Right now i only have Sun's declination data and its longitude, with which i can plot only  one point, but ecliptic line is like sine wave as i read on the internet. How can i get the data of complete ecliptic line for a given day and time. I am kind of new to this, kindly apologise if my question is wrong and show me the right way.


texts: How can white dwarf form Oxygen ? (Temperature problem)

texts:
I’ve got a question about white dwarfs and oxygen.

I read in a book that a temperature of 100 million degrees is required to fuse Helium in the core of a red giant. The Helium fuses into Carbon by the triple-alpha process.

It’s also written that, after a temperature of 350 million degrees is reached, the core of a red giant ceases to be degenerate. So, the core is able to expand and its temperature is controlled. The core won't reach a temperature of more than 350 million.

But my teacher has said that a temperature of 600 million degrees is needed to form Oxygen from Carbon: Carbon fuses into Neon and by photodisintegration gives Oxygen.

So, how can there be Oxygen in white dwarfs, if we don't reach a temperature higher than 350 million degrees? By what process can oxygen be formed in a red giant?


texts:
So, in school (that's a long time ago) they have been teaching us there are 9 planets in our solar system.

Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto

But every now and then I keep reading stories about another "dwarf planet" (Eris, discovered in 2005) that - depending on what source tells the story - is another planet according to the astronomical definition, while other sources say that it isn't a planet. Some even say Pluto isn't a planet anymore either.
The result: I'm confused due to the contradicting stories. Even Wikipedia isn't clear about Eris and only writes (emphasis mine):

NASA initially described it as the Solar System's tenth planet.

Initially? So, is it a 10th planet or not? Fact is, there is another "something" out there and it surely seems to look like a planet. Yet, some people keep stating there are 9 planets in our solar system, while others say there are more than 9 planets, and then again there are people stating that the latest definition of "planet" has kicked out Pluto too so there are actually fewer than 9 planets in our solar system.
Trying to get a definite, official, and astronomically correct answer I can actually rely on, I'm therefore asking: How many planets are there in this solar system?
EDIT
The "Definition of planet" at Wikipedia doesn't really help either, as it states:

Many astronomers, claiming that the definition of planet was of little scientific importance, preferred to recognize Pluto's historical identity as a planet by "grandfathering" it into the planet list.*
* Dr. Bonnie Buratti (2005), "Topic — First Mission to Pluto and the Kuiper Belt; "From Darkness to Light: The Exploration of the Planet Pluto"", Jet Propulsion Laboratory. Retrieved 2007-02-22.

So, if you link somewhere to provide proof, it would be great if you could point me to a more trusted source than Wikipedia. Ideally, an astronomical trusted source and/or paper.


texts: Why does the sun have a convection layer and a radiation layer?

texts: Why is the outer section of the sun convective but the inner section stable and only radiative? They are both made up of the same kind of matter, both heated by the core.


texts:
The $r$-process in supernovae happens when a high flux of neutrons irradiates the heaviest abundant nuclei (in the region of iron), resulting in endothermic nuclear reactions.

To the extent that at least some of the highest $r$-process elements are now thought to be synthesised in neutron star mergers, is the mechanism the same: that is, is it a question of  the (hypothesised) iron crust of the neutron stars being irradiated by a sudden intense flux of neutrons at the moment of the merger? Or is it that the "splashed" neutronium resolves itself into a range of atomic nuclei, especially the heavier $r$-process ones?

I appreciate that this is a question about hypothesis built upon hypothesis, but it would be interesting to get some idea of current thinking.

EDIT (from a comment): This Stack Exchange answer suggests that splashed neutronium will end up as the lightest elements, but tantalisingly raises another interesting question: whether the $r$-process elements are created in the merger or whether they are constantly present at the bottom of the crust, in some sort of equilibrium between the infinite supply of neutrons within the star and the iron in the crust itself. In which case the merger would create nothing, merely liberate what is already there.


texts: Is there a non-trivial limit to a number of nested orbits?

texts:
In his popular youtube channel, Scott Manely addressed a question of whether an astronaut can orbit a space station. The provided answer is negative since such an orbit would require the space station to be impractically dense.

This got me wondering if similar arguments can limit the number of nested orbits in general. For example, say you are free to choose any solid bodies A, B, C,... s.t. A orbits B, B orbits C, etc. Is there a maximal number of such bodies and do we know it?


texts: From what distance can one object influence gravity of another object?

texts: Each object in the universe has its own gravitational influence on all other objects in the universe. What distance do they have to be from each other to create only one gravitational influence? Example - Every human does in my opinion contribute to the earth gravitation thanks to the mass of our bodies. Now would there be a difference if I distanced myself from the surface by any amount?


texts: Low mass cut-off for the Dharma Planet Survey's detection of habitable planets around 40 Eridani A?

texts:
News of the discovery of a potentially habitable planet around the star 40 Eridani A (about 16 light-years away) is interesting for reasons including a 1991 letter described below in Sky & Telescope's recent article Super-Earth Discovered in (Fictional) Vulcan System, part of which is shown below.
Question: Is there any way to estimate a low mass cut-off for the Dharma survey for this particular star? Could there also be a 1 or 2 Earth mass planet there as well, within a habitable zone, as-yet undetected? Or does data there exclude this possibility?
The paper about the recent discovery: https://arxiv.org/abs/1807.07098

Almost three decades ago, Gene Roddenberry (producer of the Star Trek universe) wrote a letter to Sky & Telescope, along with Harvard-Smithsonian Center for Astrophysics astronomers Sallie Baliunas, Robert Donahue, and George Nassiopoulos. In their Letter to the Editor, they argued that 40 Eridani A — an orange-ish star 16 light-years away — would make the ideal home for Vulcan, the home planet of Science Officer Mr. Spock.
Now, a new discovery puts a little more science into that science fiction assertion.
A Long-ago Letter
In the July 1991 issue, the three astronomers and one movie-maker made the case for what star should be considered Vulcan's home:

The star around which Vulcan orbits was never identified in the original series or in any of the feature films based on it and so has never been officially established. But two candidates have been suggested in related literature.

Two Star Trek books named the star 40 Eridani A as Vulcan's sun, while another publication named Epsilon Eridani instead. However, Roddenberry and the astronomers made an argument for 40 Eridani A:

We prefer the identification of 40 Eridani as Vulcan's Sun because of what we have learned about both stars at Mount Wilson. . . . The HK [Project] observations suggest that 40 Eridani is 4 billion years old, about the same age as the Sun. In contrast Epsilon Eridani is barely 1 billion years old.

Based on the history of life on Earth, life on any planet around Epsilon Eridani would not have had time to evolve beyond the level of bacteria. On the other hand, an intelligent civilization could have evolved over the aeons on a planet circling 40 Eridani. So the latter is the more likely Vulcan sun. . . . Presumably Vulcan orbits the primary star, an orange main-sequence dwarf of spectral type K1. . . . Two companion stars — a 9th magnitude white dwarf and an 11th magnitude red dwarf — orbit each other about 400 astronomical units from the primary. They would gleam brilliantly in the Vulcan sky.


texts: Say we were to bring Titan to Earth's orbit. How much would its atmospheric pressure change?

texts:
I've heard one of the reason why Titan has such a thick atmosphere is because of its really low temperature. So say that were were to magically bring Titan to the Same orbit as Earth, and the moon starts to rapidly heating up. How much of its atmosphere would it lose? Would we still be able to stand there without a pressurized suit? Is it possible to terraform Titan to the extent that we can heat up its surface while still retaining its thick atmosphere?

Thanks


texts: Detecting anomalies from the sun from home

texts:
I was wondering if there are any ways for some amateur to detect let's say solar flares or CMEs from home. What kind of hardware would you need in order to have chance of seeing/measuring those?

I have a background in programming software and I've gotten my feet wet in hardware if that's of any help.

I'm aware that the weather plays a "bit" of a factor and I am sure that I can't afford a satellite but anything is welcome!


texts:
According to

Tidal locking

  The effect arises between two bodies when their gravitational
  interaction slows a body's rotation until it becomes tidally locked.
  Over many millions of years, the interaction forces changes to their
  orbits and rotation rates as a result of energy exchange and heat
  dissipation. When one of the bodies reaches a state where there is no
  longer any net change in its rotation rate over the course of a
  complete orbit, it is said to be tidally locked.

Is there any planet or satellite in the solar system in the process of getting tidally locked?


texts: Why doesn't Earth's axis change during the year?

texts:
My understanding is that the Earth's axis points in the same direction in space during its entire orbit around the sun. And this is what causes our seasons.

My question is why doesn't the axis follow the orbital path (kind of like a car driving around a circle)?

I imagine the Moon plays a part in this.

As a secondary question, do the other planets in our solar system orbit the same as Earth (its axis points in the same direction in space for its entire orbit)?


texts: How many satellites orbit their planet faster than the planet rotates?

texts:
Phobos is so close to Mars that it orbits Mars much faster than Mars rotates. This means that it rises in the west and sets in the east, even though its orbit is prograde.
Are there any other known natural satellites that orbit their planet faster than the planet rotates, or is Phobos unique in this regard?


texts: Estimating galactic dust extinction for medium band filters

texts:
I have a set of medium-band filters and I would like to compute $A_{\lambda}/E(B-V)$ for each filter which are not reported in the literatures. The magnitudes of the objects in the photometry catalogue should be corrected for the galactic dust extinction using Cardelli et al. 1989 law.

Update

In appendix B of D.J. Schlegel, D.P. Finkbeiner, & M. Davis (1998, ApJ, 500, 525) estimating the $A_{\lambda}/E(B-V)$ for filters is obtained by using this equation
$$
\Delta m_f=-2.5\frac{\int d\lambda W_f(\lambda)F(\lambda)10^{\frac{-A(\lambda)\Delta m_V}{2.5}}}{\int d\lambda W_f(\lambda)F(\lambda)}
$$
$\Delta m_V$ is the reddening magnitude of an elliptical galaxies and $F(\lambda)$ is the flux of source and $W_f(\lambda)$ is the response function of a filter. I am wondering how I can use  Cardelli et al. 1989 law to estimate these quantities for different filters or there is an alternative approach?


texts:
I have been reading the OMNIWeb data documentation in order to clarify one particular question without success. I need to associate each measurement in the OMNI dataset to a moment in time at the sun (at least to narrow it to a time interval). Therefore, I need to understand how long it takes for the solar wind to get from the sun to the point where it is measured. I understand that the solar wind velocity is variable, so this time interval is constantly changing.

Could you please help me understand this question? Can the solar wind measurements be used to trace back into the moment at which it left the sun? I would be very grateful if you could explain or point me to some sufficient references.


texts: Is there any cosmological evidence that neutrinos travel at a speed other than c?

texts:
I've been looking into neutrinos. One thing I'm puzzled about is how fast they travel.

See the Wikipedia SN1987A article where you can read this: “approximately two to three hours before the visible light from SN1987A reached Earth, a burst of neutrinos was observed at three separate neutrino observatories”. Some reports describe an initial burst of neutrinos which arrived 7.7 hours before the light. It's thought that the neutrinos were emitted before the light because of the way stars collapse, wherein photons take longer to get out. I don't have much of an issue with that. But what's interesting is that in 168,000 years travelling through space, the photons didn’t overtake the neutrinos. That suggests to me that neutrinos are massless, which ties in with what Fermi said in section VII of his 1934 paper. He plotted three curves and noted that the μ=0 curve matched the empirical curves. He concluded that “the rest mass of the neutrino is either zero, or, in any case, very small in comparison to the mass of the electron”.

The thing is that if neutrinos travel at exactly c they have no mass at all. And I can't find any evidence that they don't. I can find plenty of evidence for electrons travelling at speeds less than c. The neutrino is said to be a fermion like an electron. But I can't find any evidence of neutrinos travelling at speeds less than c.

Can anybody give me a reference to any cosmological evidence that neutrinos travel at less than c? Or any other hard scientific evidence? By evidence I don't mean an inference such as "neutrinos go missing so they must oscillate therefore they must have mass therefore they must travel at less than c". I mean evidence.


texts: I've stumbled across several articles about how the Venusian polar high atmosphere is really cold. What these articles appear to fail to specify is what the surface temperatures of the poles are. I am interested in knowing the polar surface temperatures. I would think that convection would lower the polar surface temperature to lower amounts, but I don't know a lot about Venus's poles to say anything about this.


texts:
It always amuse us to research about things around us and we always start our research with a question that - what must be the reason for happening of that phenomenon?

As we know that the formation of universe is being postulated with theory of Big Bang.
But now, I want to ask that what was the reason for Big Bang. I mean why it happened, what must be the circumstances or what made it happened?


texts: What Right Ascension and Declinations are observable by a telescope from a particular location?

texts:
I'm new to Observational Astronomy, and I just started observations with a telescope and read about RA and Declination(celestial co-ordinates). Although I think I understood the concept, I'm confused about what RA/Dec is visible from the location at present(Summer Sky).

From what I have understood, since I'm in Sendai, Japan(~38.26N, 140.86E), the +38 degree declination is at my zenith at midnight. So almost -30 Declination will be at my horizion. That should mean that I can see stars from -30 Declination to 90 Declination at my location. Is that correct?

What about RA though, what range of RAs will it be possible to view while its dark(2000 hours to 0300 hours)


texts:
As pointed out in this answer the axes of galactic coordinates are defined such that galactic longitude and latitude (0, 0) point toward the galactic center. But then the plane defined by galactic latitude equal to zero would be parallel to the galactic plane only if the Sun were in the galactic plane as well.

Is that the case?

More generally, by what procedure was the galactic plane actually defined, considering a substantial part of it is obscured by dust (at least in the visible) and most of the mass is dark matter and therefore not observed at all (directly at least)?

Question: How was the galactic plane established? Primarily what kinds of observations were used, and how were they analyzed to help decide how this plane should be chosen?


texts:
Wikipedia says that there are now 67 known moons of Jupiter.

It got me wondering: is it really possible in our day and age that there are more, but we haven't observed them yet?

On the other hand, there is a Jovian moon discovered as recently as in 2011, so I wouldn't be amazed if the answer was 'yes'.

Really though, choosing Jupiter for this question was a bit arbitrary on my part, as the same question can be asked for other more distant and bigger planets of our solar system, like Saturn.


texts: Are exoplanets which are above escape velocity of particular interest?

texts:
I was perusing the exoplanet database and looking for some of the more extreme orbits, when I happened upon HD 20782 B:

http://exoplanets.org/detail/HD_20782_b

Which is also listed (in two sentences) on wikipedia, so there's not a whole lot of information. However, the first thing I noticed was that it was almost at escape velocity!

I guess not much is known, but my overall question is:

Would an exoplanet on an escape trajectory offer us any opportunities for research that have yet to be performed? What would those opportunities be? The answer can be a justified no (E.G. once the planet leaves the host star, we can't observe the doppler shift anymore).

Imaginary Bonus Points: have there ever been any observed as escaping/becoming rogue planets?


texts: Adjective for things outside our solar system

texts:
I know we have "exoplanets" etc. but those are nouns for specific objects outside our solar system.

We have extraterrestrial for objects outside Earth's atmosphere, but I don't know if we have a general adjective for objects outside our solar system.


texts:
How are redshift, (recessional) velocity and distance of a galaxy related?
I understand what v=HD states. So I assume that Hubble measured a direct relation between the distance and recessional velocity of a galaxy.

I get confused about the relation between the redshift and the other two. Is there a direct relation between the redshift and the distance and between the redshift and the velocity of a galaxy?


texts: What is the difference between a dwarf spheroidal galaxy and a globular cluster?

texts: This Wikipedia article states that Segue 1 is either a dwarf spheroidal galaxy or globular cluster associated with our own Milky Way.  I am wondering what the difference is between dwarf spheroidal galaxies and globular clusters, since at first glance is seems that the morphological properties and stellar ages are similar between the two classes of objects.


texts: Obtain tangent point (origin) of the Standard Coordinates system

texts:
In a previous question (Transform pixel coordinates (in FITS file) to equatorial), Rob supplied a great source that describes the process of obtaining celestial coordinates for objects in an observed field.

The source mentions the tangent point in its description of the Standard Coordinates system:

  These are the projection of the RA and DEC of an object onto the tangent plane of the sky, i.e., the plane tangent to the sphere of the sky that intersects the sky at the tangent point (which is usually somewhat offset from the image center). The X coordinate is aligned with RA and the Y coordinate is aligned with DEC. The origin of the standard system is at the tangent point in the image.

I would've assumed that the tangent point (ie: the origin of the standard coordinates system) would be located at the center of the observed field. Apparently this is not correct, hence the questions:

Why is the tangent point usually offset from the image center? (See Edit below)
How is the tangent point $(\alpha_0, \delta_0)$ obtained?

Edit

I've found the answer to the first question in The Handbook of Astronomical Image Processing, Berry, R. & Burnell, J. (Willmann-Bell, Second Edition 2005).

In Chapter 9 of this book, Astrometry is discussed. Standard coordinates are introduced in page 253 and the effects that disturb the tangent point $(\alpha_0, \delta_0)$ are discussed in page 254:

  In real life, however, $(\alpha_0, \delta_0)$ is inevitably somewhat off the center of the image, and the x and y axes of the detector will be rotated through some angle. (...) In addition to displacement and rotation, the detector might be slightly tilted relative to the incoming light; the manufacturer's figures for the pixel dimensions might be slightly inaccurate at the CCD's operating temperature; and in the case of scanned photographs, the axes may not be perfectly orthogonal and equally scaled.

(Figure 9.2, copyright of the Authors)

However, in page 258 (after explaining how to obtain X,Y from known positions of reference stars in the frame) the authors convert the X,Y coordinates to equatorial coordinates assuming that $(\alpha_0, \delta_0)$ are "now known".

I might have missed something obvious, but I don't see where these coordinates are obtained in the preceding pages. Question 2 thus, still stands.


texts: What lies at the center of a neutron star if any?

texts: What does the current theory tell us about what is going on at the core of a neutron star, I'm expecting a black hole hopefully I won't be disappointed!


texts: How can I hear (or at least detect) a pulsar at home?

texts:
Scott Manley's video Using Relativistic Raytracing &X-Rays To See Detail on Surface Of Neutron Star talks about X-ray measurements using the NICER X-ray telescope attached to the International Space Station (Wikipedia, in SE: 2 & 3), results which can also be read about in arXiv and these recent papers. Since I'm on Earth I'll need to use radio waves instead.

I understand the signal will be weak and below the noise for a small setup so I'll have to collect a lot of data and do some type of folding analysis. But before I can even make an estimate of signal and noise levels I'll need to choose a few "strong" pulsars and go look up their radio spectral distribution and compare it to thermal and and sky noise spectra.

Also based on frequency I can then know better what kind of antenna can be used; if I can get away with an array of wires like the early days or I'd need a dish.

Is there something like a "Top 10 pulsars of all time" site which has a characterization of some "popular" objects that may have strong signals that would also list their period?

Are there other issues I might not have thought about yet?


texts: Is there any proof of space being created?

texts:
Is there any proof for space being created?

Because I guess an explanation for the dark energy (dark = our understanding of it) could be that there is a gigantic amount of matter/dark matter that we cannot see (the gray clumps in the picture) that are attracting our matter (the known universe in the middle) => of course the universe is "expanding" with an acceleration.

Am I talking non-sense?


texts: How to get error out of astropy constants

texts:
How do I get the error value out of an astropy.constants quantity?

In [87]: from astropy import constants as c

In [88]: c.M_sun
Out[88]: <Constant name='Solar mass' value=1.9891e+30 error=5e+25 units='kg' reference="Allen's Astrophysical Quantities 4th Ed.">

In [89]: c.M_sun.value
Out[89]: 1.9891e+30

In [90]: c.M_sun.error
AttributeError: 'Constant' object has no 'error' member


texts: Could FRB be the result of matter-antimatter annihilation?

texts:
I was listening to a scientific podcast about CPT-symmetry and mirror-universes, and when speaking about matter-antimatter annihilation, they stated that several emissions would occur at this time, notably gamma rays.

So this raised that question to me: I know that FRB (Fast Radio Bursts) are theorized differently today (lifecycle of some stars, etc.) but, could they actually be the result of matter-antimatter annihilation occurring locally (i.e. a bunch of matter colliding another bunch of matter)? After all, matter cohabiting with antimatter has been one theory, but we failed to find evidence of it... unless it is FRB.

Note that this is a newbie question and I'm not convinced of that, but would rather know why this cannot be the case (like, "we have solid proof of what FRB are", or "the matter-antimatter emissions would not be the same as the ones in FRBs", etc.).


texts: Gravitational field released during supernovae

texts: During the collapse of a star at the commencement of supernovae, the intense pressures force fusion and fission to create the heavier elements and release vast amounts of energy. As this energy/mass is released - the gravitational field must also decrease in an instant, and as this "Warping of space time" is instantly released and returns to flat space (Or flatter space) - does this create or contribute to the explosion of the supernovae itself? I have always been puzzled by the concept of the collapsed outer layers "Bouncing off of an in-compressible core" as the source of the explosion. Isn't this instantaneous "Relaxation of the curvature of the space" not what we see as the explosion?


texts:
In Isaac Asimov's Foundation series, the main characters are looking for the long-lost Earth. There are two major features of the solar system that seem to make it unusual among the millions of inhabited systems: the rings of Saturn and the size of the Moon.
The conversations below are mostly between Golan Trevize, ex-military, well-versed in astronomy, and Janov Pelorat, a naïve and recluse history teacher.
The rings of Saturn

"That's what the poem was speaking of. Three wide rings, concentric, wider than the planet itself."
Trevize said, "I never heard of such a thing. I don't think rings can be that wide. Compared to the planet they circle, they are always very narrow."

"Is that sort of thing common?" asked Bliss, awed.
"No," said Trevize. "Almost every gas giant has rings of debris, but they tend to be faint and narrow. I once saw one in which the rings were narrow, but quite bright. But I never saw anything like this; or heard of it, either."
Pelorat said, "That's clearly the ringed giant the legends speak of. If this is really unique-"
"Really unique, as far as I know, or as far as the computer knows," said Trevize.

The Moon

"A giant satellite is more difficult to accept. No other inhabited world in the Galaxy has such a satellite. Large satellites are invariably associated with the uninhabited and uninhabitable gas-giants. As a Skeptic, then, I prefer not to accept the existence of the moon."

"Yes. It's rather farther from the planet than one might expect but it's definitely revolving about it. It's only the size of a small planet; in fact, it's smaller than any of the four inner planets circling the sun. Still, it's large for a satellite. It's at least two thousand kilometers in diameter, which makes it in the size range of the large satellites that revolve about gas giants."
"No larger?" Pelorat seemed disappointed. "Then it's not a giant satellite?"
"Yes, it is. A satellite with a diameter of two to three thousand kilometers that is circling an enormous gas giant is one thing. That same satellite circling a small, rocky habitable planet is quite another. That satellite has a diameter over a quarter that of Earth. Where have you heard of such near-parity involving a habitable planet?"
Pelorat said timidly, "I know very little of such things."
Trevize said, "Then take my word for it, Janov. It's unique. We're looking at something that is practically a double planet, and there are few habitable planets that have anything more than pebbles orbiting them. Janov, if you consider that gas giant with its enormous ring system in sixth place, and this planet with its enormous satellite in third—both of which your legends told you about, against all credibility, before you ever saw them-then that world you're looking at must be Earth. It cannot conceivably be anything else. We've found it, Janov; we've found it."

Quotes are from Foundation's Edge (1982) and Foundation and Earth (1986).
My question is in two parts:

Are the various descriptions and facts given above generally correct?
How unusual are Saturn's rings and the Moon compared to other systems we've observed?


texts: How much damage would collision with a similar mass primordial black hole do to earth?

texts:
All this talk of Planet 9 perhaps being a primordial black hole (PBH) made me wonder how dangerous a PBH collision with earth would really be.

Specifically, if earth collided with a PBH of 1 earth mass, traveling fast enough that they didn't end up orbiting each other, what would happen?

Edit:
From a paper asking Can one detect passage of small black hole through the Earth? the analysis was that for an approximately proton-volume and mountain-mass sized PBH

  "It creates a long tube of heavily radiative damaged material, which
  should stay recognizable for geological time."

but is otherwise pretty hard to detect.

What would change if the PBH were the mass of the earth and the volume of a large marble? How slow would it have to be going before it really messed things up?


texts:
I have a masters degree in computer science and statistics but would like to advance my knowledge in astronomy, ideally in getting some kind of online degree.

Does anybody have experience, suggestions or recommendation where I can do what without having to be physically present at a university?

Also, I would like to get view on what specific topics in astronomy it would make sense to focus if my skills are mainly in computer science and data analysis?


texts:
Diamond Fuji is a phenomenon in which the (typically) setting sun is positioned directly atop Mt Fuji. Some relatively detailed predictions for viewing times at a nearby park are available here.

I will be traveling to Tokyo in early December, and would like to observe Diamond Fuji to the extent possible (if at all). I can rely somewhat on tourist-friendly websites, but information is sparse and imprecise.

Intuitively, one should be able to compute the time and viewing locations of Diamond Fuji for any day of the year: the summit of Mt Fuji lies on the line connecting the viewer to the sun. What is the best way to work out this sort of calendar/map?

As a non-expert I suspect this question is relevant but I am not certain.


texts: What is the distribution of organic compounds in the Milky Way Galaxy?

texts:
I imagine the answer is unknown for the entire galaxy, but I would appreciate a notion of the scales and locations of regions where astronomers have ventured at least a guess to the distribution of organic matter in interstellar dust.

Updated

I am specifically looking for plots showing the distribution of some selected organic compounds (doesn't really matter which ones right now) within a given section of the sky.  Or, if possible, within a given arc and range with respect to the galactic center (again, if possible).


texts: Would it be possible to detect a magnetic field around an exoplanet?

texts: Of course, we can't fly a magnetometer next to an exoplanet to measure the magnetic field, but might it be possible to find indirect evidence (e.g. polar auroras) of a magnetic field generated by an exoplanet? Has this already been done?


texts: Do all orbiting bodies eventually collide?

texts: If two celestial bodies are in orbit, will they always eventually collide if not acted upon by outside forces?


texts:
I have been given an old telescope (Newtonian, 910mm) and I got a mount for my DSLR and I'm trying to take some pictures of various objects.  In particular, I'm trying to photograph Saturn, but I'm having some difficulty getting a decent image.  This is about the best I could get:

This was taken with a 2x Barlow T-mounted to my DSLR via an extender, basically a metal tube about 2.5 inches long (without both of these my focuser doesn't have enough range unless I drop an eyepiece into the extender, then the Barlow isn't needed).  I shot on a one second delay to allow any vibration from the shutter opening to subside.  Focus was manual via the telescope itself, and was at the sharpest spot I could find.   I had been outside for some time and temperature difference between the air and the scope were minimal.

I'm wondering if there are any pointers or maybe an idea of what I might be doing wrong.  This above exposure was 1/10s, ISO 5000.  I thought maybe the ISO setting was too high, but the image below was at 1/15s, ISO 2000 and doesn't look any better:

There seems to be some chromatic effect, in the first image the upper-left side has a blue tint which works its way across the spectrum to red in the lower-left.

The scope was collimated using the star method as I don't have a tool, so it may not be perfect but it's pretty good.

The thing that I am really puzzled about is that through the lens the image did not look like either of these pictures.  Although a bit small, I could make out the variations in color and some of the texture of the planet and its rings.  The image was sharp and there were no chromatic aberations.  Aside from having the rough shape of Saturn, the pictures have almost no resemblance to what I saw right before I took the pictures.  (This is looking directly through the lens of the camera through the optical viewfinder, live preview also looks ok, but the screen resolution isn't as great.)


texts: Distance between stars Epsilon Eridani and Tau Ceti?

texts: I am working on a story. It would be helpful if someone could provide the distance in light years between star Epsilon Eridani and star Tau Ceti.


texts: How can I accurately find & apply the white donut to the center of my mirror?

texts:
I have a Plettstone 18" Dobsonian telescope and use a Howie Glatter tuBlug, laser collimator, and Square Grid Projection Attachment to adjust the mirrors.  Proper collimation requires an accurate identification of the mirror's center. I would like to hear of good methods to very accurately place a white sticky donut concentric to the mirror's optical center.

The mirror already has a donut, but I wonder if it is accurately placed as to my eye it appears slightly off center, but perhaps the optical center is not the physical center?

I've seen a recommendation in Sky & Telescope to get two clear plastic rulers that bend and place them at exact right angles to each other with the donut upside down lightly stuck to the bottom center cross point and then positioning the rulers evenly and pressing down to bend them toward the mirror and affix the donut.  However, I don't think this method is well suited for an 18" mirror, perhaps I am mistaken?

I've also seen a recommendation by Gary Seronik to make a paper cutout that matches the mirror shape and to find its center and make a small hole and then place that over the mirror and use a pen to mark the center and center the donut around the marker, however, again, I don't think this is well suited for an 18" mirror.  This method is also mentioned here in some detail, but they specifically state not for use with a laser collimator.

Please suggest how I can first gauge the existing donut for accuracy and if it is found to deviate significantly how to remove it and the adhesive and place a new one more accurately.


texts: If a star were travelling at 99% of the speed of light, directly at Earth would we see it?

texts:
Stars being flung from black holes in the news made me question if something were heading directly for us at the speed of light, would we even know?

Update: Since it's impossible for a star to travel at the speed of light, would we see it coming if it were traveling at 99% the speed of light? and if so, how much warning would we have?


texts: Is the American Astronomical Society 230 years old?

texts:
The BBC News item Light shed on mystery space radio pulses is interesting enough in its own right. But I noticed that it is reporting on news from the 231st meeting of the American Astronomical Society.

These kinds of meetings are usually annual; for example the 120th Annual meeting of the American Physical Society will be in 2019.

Were there enough astronomers in the US in 1787 to have an American Astronomical Society and it's first meeting?

If it turns out that the answer is that meetings were more frequent than annual, why would that be?


texts: Luminosity value to use for the calculation of the habitable zone?

texts:
I'm currently studying the star system of Gliese 570  and I´m trying to calculate the habitable zone of the component A from the luminosity value in relation of the Sun´s. I´ve read that the needed value of luminosity is the value of the bolometric luminosity (here 26%), but the calculations of the HZ that I found is about 0.40 AU, which seems to be calculated from the visual luminosity (about 16%).

So, the questions are: Which of these 2 values do I have to use to calculate the habitable zone? Does the stellar class of the star affect the selection of it?


texts: What would a moon with a six-month orbital period look like from the earth?

texts:
This is a kind of follow-up question to "What orbital period would produce one New Moon (and one Full Moon) each year?"
Given the six-month orbital period that is needed to produce one New Moon and one Full Moon each year, what would such a satellite look like as it made its progress through the sky (assuming we are in a system that is as close to our current situation as possible)?
In other words, I am wondering things like:

How long would it take the moon to cross the sky?
What kind of moonrise and moonset times would we expect, and how would they vary with the seasons (if at all)?
What would be the effect on tides?
What other observable effects (observable by mere mortals going about their business, that is, rather than astronomers or astrophysicists) would result from a moon with a six-month orbital period?

Grateful for any insights here.


texts:
So most nights the Moon usually rises on the right of the sky when I look through the window just like the previous night.

But this night the Moon was on the left of the sky rising. Does anyone know what this is?


texts: Which unit is most suitable in comparing needed light intensity for night reading on the Moon, vs on Earth?

texts: Which unit is best to use, and why, when determining how many times easier it is to read a newspaper (or any other printed text) on the moons surface at night under a full earth, compared with reading it outdoors on  earth during a cloudless full moon night: Albedo, Bond Albedo, Apparent Brightness, Apparent Magnitude, Geometric Albedo, Lux, or something else?


texts: Is axial tilt direction correlated with semi-major axis direction?

texts:
Earth comes closest to the Sun every year around January 3. Winter solstice is at 21-22 December, merely some 12-13 days away. That means projection of Earth rotation axis onto the plane of its orbital movement almost overlaps with its orbit's semi-major axis; the axial tilt direction coincides with the direction Earth orbit is elongated.

I couldn't find corresponding data regarding other bodies in the Solar System.

Is this merely a coincidence, or is there a regularity, with direction of the axial tilt coinciding with eccentricity of the orbit? How does that look like in case of other bodies than Earth?


texts: How variable does a star have to be, to be a variable star?

texts:
Variable stars are stars whose apparent magnitude varies. But there are so many phenomena that can cause a star to be variable, that I would expect all stars to be variable. A rotating star has a starspot? It's variable! A planet is transiting? It's variable! A cloud of dust passes in front? It's variable!

This makes me wonder what exactly distinguishes a variable from a non-variable star? Must the variations in brightness be larger than a given magnitude? Must the variations in brightness be periodic? Do dips (or peaks) in brightness be observed more than once?


texts: Do the "schwarzschild metric" or the "isotropic metric" fit the Event Horizon telescope data on Messier 87 better?

texts:
The "Schwarzschild solution" in "Schwarzschild metric" looks like:

$$\text -c^2d\tau^2=-\left(1-\frac{2GM}{rc^2}\right)c^2dt^2+\left(1-\frac{2GM}{rc^2}\right)^{-1}dr^2+r^2(d\theta^2+\sin^2\theta\,d\phi^2)$$

Using this metric you get certain values for the radius of the "Schwarzschild radius", the "photon sphere" and the "least stable circular orbit", among other things. When the Jet Propulsion Laboratory or other institutions are dealing with orbital dynamics in the solar system, they instead use the "isotropic metric" or at least a first order expansion of the isotropic metric to calculate relativistic effects on the orbits. Now the Schwarzschild solution in isotropic coordinates looks like:

$$ -c^2d\tau^2 = -\left(\frac{1-GM/2rc^2}{1+GM/2rc^2}\right)^2c^2dt^2 +(1+GM/2rc^2)^4[dr^2 +r^2( d\theta^2 +\sin^2\theta d\phi^2)]$$

Now in isotropic coordinates the "Schwarzschild radius", the "photon sphere", the "least stable circular orbit" among other things take other values.

Question 1: Now that we have the measurements from the "Event Horizon Telescope" on the black hole, can something be said about what coordinates that fits the data better?

Question 2: It might be that both metrics fit the data equally well if we change the mass of the central black hole. Do we get different values on the mass of the central black hole if we fit the data using the isotropic coordinates instead of the Schwarzschild coordinates?

According to the Schwarzschild solution in Schwarzschild coordinates the photon sphere is located at an "r-parameter" of $3GM/c^2$. According to this post when using the Schwarzschild solution in Schwarzschild coordinates the apparent radius ($r_{obs}$) of something residing in a spherically symmetric gravitational potential when viewed from infinity is: $$r_{obs}=r(1-\frac{2GM}{rc^2})^{-0.5} $$
According to this formula we will observe the photon sphere at a radial distance of $r_{obs}=3\sqrt{3}GM/c^2$. Now I assume astronomers estimate the  "observed radial distance", "$r_{obs}$" from the center of the M87 black hole to the photon sphere around the M87 black hole by measuring the angular size of the observed ring together with some estimate of the distance from earth to M87. If you use the formula for the photon sphere radius in Schwarzschild coordinates together with the formula for gravitational lensing enlargement you end up with a formula for the central mass of M87 as: $M=\frac{r_{obs}c^2}{{G3\sqrt{3}}}$.

Now if isotropic coordinates are used instead you will get another expression for the "r-parameter" of the photon sphere (I do not know what that expression looks like) and another expression for the "gravitational lensing enlargement effect" that makes objects in a spherically symmetric gravitational field look larger when observed from infinity.

What i specifically would like to know in the second question above is how much the mass of the central body will "change" if you keep $r_{obs}$ constant but you use isotropic coordinates instead of Schwarzschild coordinates and in both cases equate the "r-coordinate" with radial distance.

I am a bit confused about the concept that you can do various coordinate transformations of the "r-parameter" in the Schwarzschild solution and still get a solution that fits reality.


texts: Why does Sirius proper motion "wiggle" with a 1 year period, when Sirius A and Bs binary orbit is a 50 year period?

texts:
Some stars, if observed repeatedly over time, show a perturbation or "wobble" in their proper motion. If this is a periodic occurrence we can infer that the perturbation occurs due to the gravitational influence of an unseen companion.

In Sirius Matters, Noah Brosch describes a secondary wiggle,

"The trajectory described by the two components of Sirius shows an additional component of motion as tiny wiggles super-posed on the wider modulations of the proper motion by the orbital motion of the Sirius pair. The wiggles have a period of one year. "

What causes this second wiggle?


texts: I know that models of ocean planets typically have deep liquid water that transitions into exotic forms of ice. What I am wondering is if it makes sense to have an "ocean floor" composed of debris from bombarding asteroids during the early formation stages?


texts: Is there anything like a supermassive white hole? How are they formed? And where are they present?

texts: The idea of a 'super massive white hole' is sometimes discussed regarding GR,SR and the destination of material 'lost' in a black hole. Is there any good theoretical or observational evidence for these SWH, or are they merely metaphysical speculations?


texts: Why do we think that there is no two-solar-mass black hole?

texts:
We think that the mass boundary between neutron stars and stellar mass black holes is  around three solar masses.

The maximum mass of the neutron stars now is two solar masses and we may find a 2.6 solar mass neutron star in the future. That is based on the equation of state.

The stellar mass black holes may have different origins. Even the smallest stellar mass black hole originates in SN explosion,  we do not know the details of the explosion.

Why do not we think a two solar mass BH, or even a smaller BH, could exist?

Why do we think that the companion of Taylor-Hulse binary is a neutron star instead of a BH?


texts: What do cosmologists mean when they talk about "the running of the spectral index"?

texts: All I know is that the spectral index is related to the CMB, and that it has to be slightly less than 1 to favor inflation.


texts: How was Mars' very noticeable change in apparent magnitude explained by the Geocentric Model?

texts:
In the geocentric model, the Sun, the Moon, and the 5 naked-eye planets (Mercury, Venus, Mars, Jupiter, Saturn) all orbited Earth.
Today we know that the planets orbit the Sun, and thus they come closer to Earth at certain times than at others. This means that planets are noticeably brighter at opposition than when they're farther away.

Mercury and Venus are inferior planets and thus their change in apparent magnitude over the course of one orbit is hard to notice.

Jupiter and Saturn's orbital radii are much larger than Earth's and thus their closest and farthest approaches from Earth are not that different. This means that Jupiter and Saturn's apparent magnitudes over the course of one orbit does not change that much and is hard to notice.

However Mars' apparent magnitude very clearly varies  over the course of one orbit. It is much brighter at opposition (reaching a maximum magnitude of -2.94) than even a month later, when it is noticeably dimmer. This is also further exacerbated by the opposition effect.
How did the ancient cultures who believed in the geoentric model rationalize Mars' change in brightness? Surely they must have made the correlation that it is brightest when opposite to the Sun in the sky?


texts: Are there any planets not orbiting a celestial body which can support life despite the temperature? Also what is the absolute minimum temperature that life can survive in?


texts: Schechter Luminosity Function fitting plot of galaxies

texts:
I would like to plot the Schechter Luminosity function of galaxies. Here is my data(I have the Luminosity L[Ha] in erg/s).
I would like to plot like this figure from this paper.
In this paper, they used these equations for the plotting(there are four datasets in this case, but for my case, I want to plot only my data).

I used python to plot the function. Here is my code. But, I am not able to plot it. Kindly do help me with this. Also How to do the fitting with my data to get the required parameters.
import numpy as np, math
import matplotlib.pyplot as plt
from astropy.table import Table
from matplotlib.colors import LogNorm
from scipy.interpolate import interp1d

data=Table.read('lum.fits')

def Schechter_Lum(L, L_star=None, Alpha=None, P_star=None):
'''
Schechter luminosity function in LUMINOSITY
number per dex
'''
ratio = L/L_star
f = P_star* np.exp**(-ratio) *(ratio)**Alpha *ratio*np.log(10.)
return(f)

#For the reference, I used this value from the paper
L_star=42.64
P_star=-3.32
Alpha= -1.75

schechter_lf=Schechter_Lum(data['ha_luminosity_log'],L_star,Alpha,P_star)

plt.plot(data['ha_luminosity_log'],schechter_lf)
plt.yscale('log')
plt.title('H$\alpha$ Luminosity Functions')
plt.xlabel(r'Log (L[H$\alpha$]) erg/s', fontsize=14)
plt.ylabel(r'$\varphi$(logL) per $Mpc$^{-3}$ per logL',fontsize=14)
plt.tight_layout()
plt.show()

I am not able to get the figure properly and I am not able to perform fitting of my Luminosity function. Kindly do help with this. Thank You.


texts: Given the phase of a planet or satellite, I can find the area illuminated visible to us, if we consider a 2D surface. But how do I find the percentage of illuminated area visible considering it a 3D surface and thus finding the magnitude of the partially illuminated planet/satellite.


texts: My husband and I are trying to figure out what type of telescope to get our young daughter. We would like to be able to see planets but nothing too extreme. Just something to get her started. She has shown a big interest in astronomy and we would like see if it sticks then we will get her a much better one. Any suggestions?


texts: 6th catalogue of orbits of visual binary stars

texts:
I wanted to download or access the US navy catalog " the sixth catalog of orbits of visual binaries". I have already tried USNO web site and vizier. but I couldn't see them there. The link was dead for me; on www.usno.navy.mil, I reached the page but could not open the link.
Is there any other site with downloadable or accessible data on the above-mentioned catalog available?


texts: How often are there lunar eclipses on Jupiter

texts:
For the Earth-Moon system, the orbit of the Moon is at a slight incline compared to the plane of the ecliptic. This incline is enough for there to be eclipses roughly twice a year rather than every lunar month.

But Jupiter is much bigger, so its shadow is bigger also. So it seems more likely for a satellite to go into its shadow. How often does this happen?


texts: I am having trouble finding the quality of old telescopes. My question is how does a decent modern telescope that cost about a couple hundred USD compare to the top-notch telescopes in the nineteenth century. Can one make the same observations now with such a modern telescope as one could do in the nineteenth century with a top-notch one?


texts: Ensemble average VS spatial average for a cosmological density field

texts:
I'm studying statistical properties of a cosmological density field and I have some doubts; in the following quote and pictures you can see what my problem is:

  A fundamental limitation arises in cosmology – because there is only one universe to observe, i.e. there is only one realization of the stochastic process that generates the fluctuations whose consequences we observe. Therefore we cannot measure ensemble averages
  or expectation values, as we would in a repeatable laboratory experiment. What we can do when observing a fluctuation on a given scale $\lambda$ is to average over many distinct regions of size $\sim\lambda$. An ergodic-type hypothesis allows us to replace the ensemble average by a spatial average over these regions. (see pag 307 from Relativistic cosmology-George F.R. Ellis, R. Maartens, M.A.H MacCallum; Cambridge University Press (2012))

So here we talk about an average over many distinct regions of the Universe (someone call them "fair sample" of the Universe if I understood correctly) and an ensemble average is replaced by a spatial average over these regionS. Thus I should average the field over region 1, region 2 and so on and I would get many mean values of the field.

But in this presentation things seem different:

Here instead we talk about an average over an ensemble replaced by a spatial average over one realization of the random field (one of the possible  universes I imagine). In this case I have only one realization: our Universe, so I should average my field spatially over the entire Universe. And what about the regions mentioned above?

I'm confused and I would appreciate an explanation.

Thanks.

Addendum

So theoretically if i wanted to get the average of a stochastic field or of a function, we say $\delta(\vec x)$ or $f[\delta(\vec x)]$, in a point $\vec x_1$ I should do the average over the ensemble of all the universes using (see slide): $\int{\delta}\cal P(\delta) d\delta$ (it is obviously impossible because we have only one Universe). I have imagined this thing thinking about a stack of planes representing the different universes of the ensemble and drawing the point $\vec x_1$ in each plane. Now i can take the value of $\delta(\vec x_1)$ in the first universe, in the second, and so on and finally make the average of these values; if I repeat this procedure for all the points I'll get the average of $\delta (\vec x)$, i.e. $\langle\delta\rangle$ over the ensemble of the universes. Ok it's fine...but it is not possible because I have only one Universe, so I have to appeal to Ergodic Hypothesis (really a spatial version of the Ergodic Hypothesis).

  An ergodic-type hypothesis allows us to replace the ensemble average by a spatial average over these regions

It seems that I have to divide the Universe in regions (we can imagine squares for simplicity in two dimensions, I thought the Universe like a chessboard) and I can replace the ensemble averege with a spatial average over any single region. Any square of the chessboard is a fair sample of the Universe, so I have many squares that can "reproduce" the Universe (I divided my sky in many regions and I can consider these squares like the realisations of the "Universe experiment", the outcomes of the experiment). Thus I can do:

$$\langle\delta\rangle=\frac{1}{\sum_i V_i}\sum_i \langle\delta\rangle_{V_i}$$

where $\langle\delta\rangle_{V_i}=\int_{V_i}\delta(\vec x) d\vec x^3$.


texts: Parts of the Universe Shows Fewer Named Stars

texts:
I'm becoming interested in the currently identified stars in the universe. There is a wide swath where much fewer named stars are shown. Why is this?
The image below is a mollweide projection of the universe, with the earth at its center. It shows about 230,000 named stars located at their right ascension/declination points.


texts: How can the Earth and the Moon be in synchronous rotation if the Moon won't be in geostationary orbit?

texts: It is said that the Moon moves away from Earth and that during the Sun's red giant or white dwarf phase the Moon will be about 40% farther than now and in a synchronous rotation ("hantle rotation") with the Earth, meaning it will always be above the same location on Earth, like Pluto-Charon. But how would this be possible if the Moon wouldn't be in a geostationary orbit which is 35,786 kilometers (22,236 miles) above the Earth's surface?


texts: Is there a way to estimate the age of M dwarf stars?

texts:
Wolf 1061 (only 13.8 ly away) was recently found to have three rocky planets one of which is in the habitable zone. It was stated on the english wikipedia site that it has a very stable light curve and was not found to have "any significant activity such as sunspots or flares."
Would this imply that this star is very old? The expected lifetime of this M dwarf with a mass estimated to be 0.25 solar mass could potentially reach a trillion years.


texts:
This answer says that some models describes the universe as finite. How do those models describe the universe's border?

Does the border (theoretically) exist?
Is it a solid border? Do they predict what happens if matter crosses this border (maybe it simply can't)?


texts: Why does a hot cloud need more mass to collapse?

texts: I was wondering why does a hot cloud need more mass to collapse than a cold cloud to form a protostar? Is it because there's a higher thermal pressure inside the hotter cloud than it is in a colder one?


texts: What is the difference between Steinhardt's and Neil Turok's cyclic cosmology and Guth's inflationary model and Hartle, Hawking no boundry cosmology?

texts:
I have been reading some cosmology and need to ask the experts at this point some specific points. I must admit I am a little confused.

There are a few models of the universe and may be necessary at this point to see if I can sort out the main differences.  In particular James Hartle and Hawking's no boundary quantum state origin of the universe. I believe there may be some minor slight of hand imaginary time element to this to explain away a definite beginning point.

Does this theory compete with the "standard" inflationary model by Allan Guth, the one with the inflaton field and infinite inflation complete with multiverse?

There is also Paul Steinhardt and Neil Turok who are not warming up on inflation, and each propose a cyclic model. Are these cyclic models the same?

Do any of these models overlap the string theorists  "big bangs" from colliding large extra dimensions called "Brains"?

Are cosmologists these days heading in any definite direction with some of these complex and difficult for the layman to get a handle on?

P.S. I didn't mean to leave Penrose out of this , he worked with Hawking for some time when Hawking was working on his cosmological theories but I do not know which theory Penrose proposed apart from saying that his lectures appear to shy away from inflationary models proposed by Allan Guth.


texts: What is the temperature under the surface of Mercury?  I know at the surface the temperature varies greatly (-297 F to 801 F).  I also realize that the answer would likely depend on depth.  Do we know the temperature at any depth, except the surface?  I also realize the temperature may vary based on latitude.  I am mainly looking to see if there might be an ideal location / depth for a colony on Mercury for my game Planetary Settlers.


texts: What is the tightest orbit binary planets can orbit each other?

texts:
If there were two Earth-like planets in a tight orbit around each other, how close could they be to each other without colliding?
How quickly would they have to orbit to be stable?
Would they be habitable?
Could something similar to a Roche lobe form from their atmospheres?


texts: Which Chandrasekhar Limit do I use? 1.39 or 1.44?

texts: Different sources online say that the Chandrasekhar Limit is either 1.40 or 1.39, or 1.44 solar masses. Why the discrepancy? I heard it might have to do with the composition of the white dwarf, but, correct me if I'm wrong, don't pretty much all white dwarf stars have the same composition?


texts: If the Moon were impacted by a suitably sized meteor, how long would it take to impact the Earth?

texts:
An answer to the question of How well would the Moon protect the Earth from a Meteor? mentions as a possibility that the Moon could get knocked into the Earth.

What is the smallest change to the orbit of the Moon from being impacted by a large meteor that would cause it to eventually impact the Earth (i.e. "circling the drain")? What timeline would that look like (minutes, hours, days, years, etc)?


texts:
I'm trying to simulate Earth's orbit using 2nd Newton's Law and cartesian coordinates. The program seems ok, but when plotting graph, it's a parabola.

I know the shape of orbit changes according velocity. I'm using vy0 = sqrt(G*M/R) and it supposed to be an circle.

(Sorry the bad english)

Here's the code:

'-------------------Bibliotecas Importadas-------------------'

import math
import matplotlib.pyplot as plt

'-------------------Listas Criadas-------------------'

pos_x = []
pos_y = []
vel_x = []
vel_y = []
teo_virial = []
tempo = []

'-------------------------- Definição de Funções -----------------------------'

def velocidade_atualizador(velocidade_inicial, aceleracao):
    velocidade = velocidade_inicial + (aceleracao * dt)
    return velocidade

def tabela(nome, lista):
    arquivo = open(nome + '.txt', 'a')
    for i in range(len(lista)):
        arquivo.write(str(lista[i]) + '\n')
    arquivo.close

def graph(x, y, eixo_x, eixo_y):
    plt.plot(x, y)
    plt.xlabel(eixo_x)
    plt.ylabel(eixo_y)
    plt.show()

def aceleracao_equacao(pos_1, pos_2):
    r_cubo = (pos_1**2 + pos_2**2)**1.5
    k = constgrav*massasol
    aceleracao = (k*pos_1)/r_cubo
    return aceleracao

def posicao_equacao(posicao_inicial, velocidade_inicial, aceleracao):
    pos = posicao_inicial + (velocidade_inicial*dt) + ((aceleracao*(dt**2))/2)
    return pos

'-------------------Condições Iniciais-------------------'

constgrav = math.pow(6.67, -11)             #constante gravitacional
massasol = math.pow(1.98, 30)               #massa do sol
massaterra = math.pow(5.97, 24)             #massa da terra
xo = math.pow(1.5, 11)                      #posição inicial no eixo x
yo = 0                                    #posição inicial no eixo y
vxo = 0                                   #velocidade inicial no eixo x
vyo = math.sqrt((constgrav*massasol)/xo)                               #velocidade inicial no eixo y
npasso = 10000                                #numero de passos
t = math.pow(3.1536, 7)                               #tempo total = tempo de um ano
conttempo = 0                             #contador de tempo
dt = t/npasso                               #delta t

'-------------------Laço de Repetição-------------------'

while (t > conttempo):

    ax = aceleracao_equacao(xo, yo)
    ay = aceleracao_equacao(yo, xo)
    a_modulo = math.sqrt(ax**2 + ay**2)

    vx = velocidade_atualizador(vxo, ax)
    vy = velocidade_atualizador(vyo, ay)
    v_modulo = math.sqrt(vx**2 + vy**2)

    x = posicao_equacao(xo, vxo, ax)
    y = posicao_equacao(yo, vyo, ay)
    r = math.sqrt(x**2 + y**2)

    energia_pot = (- constgrav * massasol * massaterra)/math.sqrt(x**2 + y**2)
    energia_cin = (massaterra * (v_modulo**2))/2
    virial = energia_pot / energia_cin

    print('x =', x)
    print('y =', y)
    print('virial =', virial)

    pos_x.append(x)
    pos_y.append(y)
    vel_x.append(vx)
    vel_y.append(vy)
    teo_virial.append(virial)
    tempo.append(conttempo)

    xo = x
    yo = y
    vxo = vx
    vyo = vy

    conttempo = conttempo + dt

tabela('Lista x', pos_x)
tabela('Lista y', pos_y)
tabela('Lista vx', vel_x)
tabela('Lista vy', vel_y)
tabela('Lista tempo', tempo)

'-------------------Gráfico-------------------'

graph(pos_x, pos_y, 'x (m)', 'y (m)')
graph(vel_x, tempo, 'vx (m/s)', 't (s)')
graph(vel_y, tempo, 'vy (m/s)', 't (s)')

Thank you very much, guys!! I was thinking but don't know what to do anymore.

After changing the code, it works. I can rest in peace now. Hahaha.


texts: Which camera body is best introduction for beginner amateur astrophotographer?

texts:
I currently own an old 1980s Celestron eight inch orange tube schmidt cassegrain telescope with tripod. I am seriously looking to dive into some astrophotography.

I also own an olympus pen epl3 camera. It's great for photos during my hikes, but not quite as versatile as an DSLR. Unfortunately, I know of no software out there which can tether this camera to my laptop. I don't have any great ideas on remotely controlling this camera to avoid shaking my telescope.
I'm thinking of getting a DSLR at some point anyway.

Is there a camera body that anyone would recommend for me?


texts: The tidal locking problem concerning Earth sized planets in habitable zone around Red Dwarfs

texts: Would twin planets orbiting around each other present a solution to tidal locking of habitable planets in red dwarf systems? It's an awfully easy equation to set up. I'm fibbing; I can't do it. I was hoping someone might show me when they get a moment.


texts: Photographing Venus with a phone through a telescope

texts:
I took a picture of Venus through my telescope (Celestron Astromaster 130eq) using a 10mm lens with a Barlow lens.

The picture isn't really good since I took it with my phone and I still don't have a camera.

Also, it isn't a matter of focus since I fiddled a lot with it.

I don't know what to do to clear the image and reduce the brightness. Should I use a filter? and which one?


texts: Would a spacecraft just go "through" a gas giant?

texts:
From my understanding of the word gas giant, it is a planet composed of entirely a gaseous atmosphere, and so planets Jupiter and onwards fall in this category.

That being said, what would stop a spacecraft from just going right through any of these planets?

For earth, a spacecraft would firstly rapidly disintegrate approaching the surface of earth, and if it happens to still have part of itself, it will collide with the surface.

For gas giants like Uranus, if a spacecraft is able to counter the gravitational forces and slow down, could it actually "go through" Uranus?


texts: Is there Kuiper belt/Oort cloud like structure in gas giants?

texts: I know gas giants have moons, just like star have planets, how about Kuiper belts or Oort Cloud? Is there any corresponding structure in gas giants? If not, why don't they have?


texts:
The temperature of the surface of the Sun (photosphere) is between 4500° - 6000° Kelvin. Inside the core, it's around 15.7 million degrees Kelvin.

In other types of stars (neutron stars, white dwarves, etc.), what is the temperature of these areas (though many do not have these same layers) and how to they compare to the temperatures of the sun?


texts: Error associated with Sersic Profile calculations?

texts:
I am working on a Bayesian analysis project for class using data I gathered some data from NASA's Sloan Atlas (http://www.nsatlas.org/). One of the variables I am dealing with is the Sérsic Index (calculated by http://iopscience.iop.org/article/10.1088/0004-6256/142/1/31/pdf).
I am wondering if there is some error associated with this value.  I hope to model each galaxies Sersic index as a gaussian, but I can´t wrap my head around what to write as the error.

Thanks for your time!


texts:
If you threw something over a certain cliff on a moon of Uranus, it would take over ten minutes to hit bottom.

By this measure, local fall time rather than absolute height, what are the near contenders to the prize for tallest cliff on a body in hydrostatic equilibrium in the solar system?  Throwing the object horizontally at a few meters per second is ok.  Not ok is throwing it beyond a tiny body's Hill sphere.  Cliffs, not spheres.

Simplifying assumptions about atmospheres and exospheres are ok.


texts: There has been research that suggests that the changing brightness of Brown Dwarves are due to bands of Iron/Silicate clouds. Several models have been made that supports that hypothesis. My question is: Which part of the model are the actual clouds? Are the clouds the bright orange bits? Or are those bright areas “breaks” in the clouds and a view of the Brown Dwarf below?


texts: Does the Sun's atmosphere have a scale height?

texts:
Much of the Earth's atmosphere has a scale height $h$ of roughly 7 to 8 kilometers such that the local density varies as $\exp(-(r-r_0)/h)$ where r is the radius vector and $r_0$ would be some reference radius above the surface of the Earth.

This works approximately, at least up to 50 km (six or seven scale heights).

The derivation of this approximation is based on a simple gas at constant temperature, and those probably don't apply to the Sun's atmosphere very well.

Nonetheless, are there regions of the Sun's atmosphere where density varies approximately exponentially in such a way that a scale height characterization would work over the range of at least a few scale heights?


texts:
Inspired by If two black hole event horizons overlap (touch) can they ever separate again?, I was wondering what would happen if two black holes collided into each other in a head-on collision.

In this model there's two black holes on a 3d Cartesian plane. Each black hole has a mass of 1 billion solar masses, and they're both going 0.9c. They're traveling on the z axis in opposite directions.

If both black holes are not spinning, one traveling positive z, the other in negative z, and collide at the origin in a perfect head-on collision what would be the result?

How long would a full merger take, and what would the resulting spin be? Would there be a large wave of gravitational energy, or some other emission?

I don't believe this to be a duplicate of Would LIGO Detect Head-On Collision? as suggested by @John Rennie or @uhoh beucase I'm more asking what's the effect on the BH themselves and what type of emissions are involved. Not necessarily ones detectable by LIGO.


texts:
The April 2015 CBS News article How NASA fixed Hubble's flawed vision - and reputation describes the modification taken to the Hubble Space Telescopes by the Space Shuttle that was used to correct for the strong spherical aberration of the primary mirror due a highly accurate but incorrect figure.

above: "Due to an oversight during fabrication, the concave shape of Hubble's primary mirror was too shallow toward its outer edges by 2 microns, a tiny fraction of the width of a human hair. As a result, starlight was not brought to a focus at the same point, resulting in blurry images. These three images show the same star as viewed from a ground-based telescope, left, and from Hubble's uncorrected mirror, center. The corrected image, after a space shuttle repair mission in 1993, is seen on the right" from here. credit: NASA
From the article:

But the mirror's biggest impact was on the Wide Field Planetary Camera, the instrument expected to provide the dazzling visible and near-infrared images most easily understandable by the public and of tremendous value to astronomers.
"The real killer was Jim Westphal (the WFPC principal investigator at the Jet Propulsion Laboratory in Pasadena, California), who tended to be very negative," Weiler recalled. "Basically, he said he couldn't do anything. So that's what I was preparing to walk into the press conference with."
But as it turned out, Weiler had two aces up his sleeve. One he knew about, one he didn't.
The ace he knew about was drawn seven years earlier, when Weiler kicked off work to build a backup camera, the Wide Field Planetary Camera 2, a carbon copy of the original. John Trauger was the principal investigator, the man in charge of the instrument at JPL.
The ace Weiler didn't yet realize was built into the design of Trauger's camera.
Shortly after the first light image came down, "one of the grand old men of optics here at JPL, Aden Meinel, he and his wife Marjorie wanted to see what the image looked like," Trauger said in an interview. "We brought it up on the screen. ... And he looked at that for five minutes and he said 'that looks like spherical aberration.'
"That was the first time I heard spherical aberration," Trauger recalled. "The thing was, he also said 'well, if it is spherical aberration, you could fix it with Wide Field Planetary Camera 2.' He knew that we had these nickel-sized mirrors in our optical system, which received a sharp image of the primary mirror itself. ... The very last mirror before the image is created on our CCD was an opportunity to straighten the wavefront out. He recognized that, too."
By giving that mirror a prescription that exactly countered the spherical aberration in the primary mirror, the WFPC 2 would be able to achieve a perfect focus and do all of the science that was intended.

Question: Where exactly is the modification that first corrected the spherical aberration in Hubble's primary mirror? Can it be identified within the image below, or is it located elsewhere? Was the modification only a change in the figure of one of the small mirrors, or were other optical elements modified as well as part of the correction?

above: "The business end of COSTAR: Small mirrors on motorized arms directed corrected light into the Hubble Space Telescope's spectrographs and faint object camera. COSTAR and the Wide Field Planetary Camera 2 were installed during a 1993 shuttle mission, correcting Hubble's flawed vision." From here. Eric Long/Smithsonian Institution


texts: Why are pseudo-Newtonian potentials used in studies of accretion processes around black holes?

texts:
In accretion processes around black holes, pseudo-Newtonian potentials are defined for the the black hole geometry. For examples, the potentials defined by Paczynski-Wiita and Artemova et al. for Schwarzschild black holes.

For Schwarzschild black holes, we already have an exact potential suitable for test particles defined by (e.g., in Shapiro & Teukolsky)
$$V_\mathrm{eff}=\sqrt{\left(1-\frac{2}{r}\right)\left(1+\frac{l^2}{r^2}\right)}$$

My Question:
Why are pseudo-potentials used when we already have an exact form of the potential? Can't we apply the above potential for accretion processes around Schwarzschild black holes?


texts: Why wouldn't massive torrents freeze on Mars?

texts:
I am currently reading the Cambridge Guide to the Solar System. In chapter 8, section 8.7, they explain that massive torrents of water created outflow channels on the surface of Mars in the past. The book goes on to state that these torrents would have been unstoppable and

Such discharges would not freeze even under
present conditions on Mars.

Yet the atmosphere of Mars is under the triple point of water, so why is this the case?


texts: What was the greatest spatial extent of the Asteroid Belt prior to the Late Heavy Bombardment?

texts:
Reading the article On the asteroid belt’s orbital and size distribution (Gladman et al. 2009), there is an interest point made:

  asteroids a
  few kilometers and smaller in size are recent collisional shards of
  larger objects since their lifetime against collisional destruction is
  much less than the age of the Solar System. As such, these bodies preserve information about collisional breakup, the dominant
  physical process that has shaped the present asteroid belt.

This suggests that there would have been a lot more asteroids etc in the main belt at the time prior to the Late Heavy Bombardment (~4 billion years ago) - which is after the major planets had formed.

My question is what was the greatest spatial extent of the Asteroid Belt in the period just before the Late Heavy Bombardment?

(I am after peer reviewed resources).


texts: Influences from outside the observable universe explaining dark energy and expansion?

texts: Could some influence from outside the observable universe be causing the expansion?


texts: Why does the distance between Sun and Earth stay the same?

texts:
Well, we all know Sun gravity , makes the  Space time curvature and space pushes the earth towards the Sun. But my question is "why the distance between the Sun and Earth is Same? Earth should have moved closer to Sun and obviously Earth should fall into the Sun."

Thanks,
Selva


texts: What are these three black cap-like pieces?

texts:
My son received a secondhand telescope for his birthday. It is a Celestron Powerseeker 114AZ.
I found these three black cap-like pieces separate from other parts. I can’t find what they are or what they do in the instruction manual.
What are they and what do they do?

(click to enlarge)


texts: What would happen if a planet is removed from the solar system?

texts:
More exactly what would to happen to us/Earth in general if any of the gas giants is removed by magic from the solar system ?

How long would it take after such change before we notice it ?

How major and would life resist to it ?

EDIT

For instance if Saturn or Jupiter is removed, what would happen ?


texts: Correlation between stellar mass and galactocentric distance

texts:
As we move away from the centre of, say, a spiral galaxy, is there a relation between the stellar mass and distance?
I know the how the stellar abundance and density varies with the distance but does stellar mass also follow a pattern?


texts:
I recently read something about a major earthquake in Japan having possibly shortened Earth's day due to an increase in rotation. Here's an example:

https://www.nasa.gov/topics/earth/features/japanquake/earth20110314.html

When I read some more about Earth's day length, I learned that the length of Earth's day is believed to have been shorter in the past and getting longer over time. Here's an example from this site:

What was the length of the solar day 73 million years ago?

As some may know from an introductory psychology course, humans tend to settle into a day that is longer than 24 hours when placed in an environment with no external time or light cues. For most people, their circadian system is able to adjust their day to the 24-hour Earth day. Some blind people lose this ability, as seen from commercials about medication to help them gain a 24-hour rhythm. Here is some background about that:

https://en.wikipedia.org/wiki/Non-24-hour_sleep%E2%80%93wake_disorder

At the risk of asking an unacceptable "opinion" question, how convincing is the evidence of historical Earth day lengths? Is the evidence at a point where shorter Earth days in the past are an accepted certainty? Or are things still at a point of being a best guess without really knowing? It would seem rather odd for our nervous systems to have evolved with a preference for days longer than 24 hours. It is certainly possible, but I would appreciate some input here before spending time contemplating why evolution might have worked that way. I'm only a hobbyist, so there would be no need to go into too much depth for me specifically. Thanks in advance.

Edit: The current answers and comments are interesting and appreciated, but to clarify, the intended focus is the extent and quality of the astronomical evidence that could be used in a discussion (elsewhere) about circadian issues.


texts: What would happen to the solar system if Earth's mass was removed?

texts:
This question is inspired by the "Stargate SG-1" episode "The Road Not Taken". In that story a device is used to shift the entire Earth to another dimension to defend against an attack.

I'm not asking about the science of whether that is even theoretically possible but rather the effect on the rest of the objects in our solar system if it did happen. Since this was apparently a short shift (likely days at the most) I would imagine there might be little overall effect to most things but it occurred to me the Moon might immediately start drastically altering its position relative to the now massless Earth (there was no indication that the effect extended to the Moon but given that ships very close to Earth were unaffected it would seen that the Moon was also unaffected) so that when the Earth returns to "normal" it may no longer be in Earth's orbit or worse, Earth may rematerialize partially within or completely around it.


texts: Get orbital period of exoplanet from light curve using astropy.timeseries

texts:
I am using astropy and I would like to calculate orbital period of an exoplanet by its star's light curve. I follow tutorial in astropy docs and I use data from Kepler in Nasa Exoplanet Archive.

There is KIC 10666592 b (expected period: 2.2 d) in tutorial, it works for me. But if I try another planet (e. g. KIC 10000941 b (expected period: 3.5047 d)), it gives bad results.

Load and plot light curve

from astropy.utils.data import get_pkg_data_filename, download_file
from astropy.timeseries import TimeSeries, BoxLeastSquares
from matplotlib import pyplot as plt
import numpy as np
from astropy import units as u

# First url is for KIC 10666592, the second one is for KIC 10000941 b.
URL = "http://exoplanetarchive.ipac.caltech.edu:80/data/ETSS//Kepler/005/755/19/kplr010666592-2009131110544_slc.fits"
#URL = "http://exoplanetarchive.ipac.caltech.edu:80/data/ETSS//Kepler/005/159/31/kplr010000941-2009166043257_llc.fits"

filename = get_pkg_data_filename(download_file(URL))
curve = TimeSeries.read(filename, format="kepler.fits")

plt.plot(curve.time.jd, curve["sap_flux"], "k.", markersize=1)

Apply periodogram

periodogram = BoxLeastSquares.from_timeseries(curve, "sap_flux")
results = periodogram.autopower(0.2 * u.day)

plt.plot(results.period, results.power)

Calculate orbital period

best = np.argmax(results.power)
period = results.period[best]
print(period)

$$\begin{array}{|c|c|c|} \hline
 & \text{KIC 10666592 b} & \text{KIC 10000941 b} \\ \hline
\text{Calculated period} & \text{2.2055172 d} & \text{13.595231 d} \\ \hline
\text{Expected period} & \text{2.2 d} & \text{3.5047 d} \\ \hline
\text{Result} & Correct & Incorrect \\ \hline
\end{array}$$

Why period for second planet is wrong? I'm doing something wrong? How can I get the correct result?


texts:
I tried to find out the magnitude in V for V* V881 Per.
Here are my results:
SIMBAD:  $11.09$    (Fluxes->V)
GSC 2.3:  $10.9815$  (VpgMag) and  $10.887$   (Vmag)
Which of VpgMag or Vmag in GSC 2.3 correpsonds to SIMBAD V-flux?
For each star GSC 2.3 cites two values for magnitude in V so which of the two should I use?


texts: How big are the chunks of rock ice that make up Saturn's rings? Are there many objects larger than pebble size?


texts:
I saw on the tv show Through the Wormhole (hosted by Morgan Freeman) that the planets in our solar system have been continuously moving away from the sun for millions of years. however, when I try to Google about it, there isn't much written about it.

Is it a proven fact that the planets are moving away from the sun?


texts: Why is the moon that special? Is it really a well built coincidence?

texts:
I find it funny that the moon is the only object in the solar system to almost perfectly fit the sun, resulting in the spectacular solar eclipses. No other object except maybe a few irregular moons like Pandora from Saturn would do that, and for them, they aren't round, and thus can't fully block out all light. The moon also has a perfect rotation that is almost exactly the same as Earth's rotational period, resulting in a tidal lock, which causes tides.

Is this a coincidence? Any speculation on why this happens? Is this the only observed place where such criteria play into such perfect coincidence?


texts:
White holes are purely hypothetical at this point and are considered only because it is assumed something like it could exist as the balance to black-holes.

Reading this article seems mostly writers taking liberties with the information but poses an interesting question.

What is a White Hole?


texts: Draw the celestial sphere for latitude, showing the star Sirius, Estimate the approximate date when Sirius rises with the Sun

texts:
I'm having trouble understanding how to solve a certain problem.

The problem is from the book Astronomy: Principles and Practice by Roy and Clarke. It is actually a solved example, but I am unable to understand parts of the solution.

  Draw the celestial sphere for latitude 30° N, showing the star Sirius (right ascension
  6h 40m, declination 17° S) at rising and draw the ecliptic. Estimate from your diagram the approximate
  date when Sirius rises with the Sun.

This is the image from the solution. I'll copy the entire solution.

Now, here's what I don't understand. If Sirius is at X, and if X is on a parallel of declination, why isn't this parallel parallel to the equatorial plane? Does the same go for the Sun? And how do we get the RA of the Sun?


texts: Is the Sun really burning and getting smaller? If so, because there is no air in space, what can be keeping it burning and what materials get burnt? If no air is required, what can speed up or can stop the burning process?


texts: Is there any correlation between the Cosmic Microwave Background (CMB) and the distribution of distant galaxies?

texts:
The Cosmic Microwave Background (CMB) is remarkably isotropic but does exhibit a distinct dipolar Doppler shift and also much smaller but measurable fluctuations in intensity and polarization.  Presumably some of these fluctuations should carry over into the subsequent formation of early galaxies and other structures.  To what extent is this expected and to what extent has this been observed?
The CMB Doppler shift is attributed to our local velocity with respect to the early universe. Is this Doppler-shift equally observed with respect to distant galaxies and diffuse starlight?
More particularly, is any of the fine structure in the CMB represented in the distribution or properties of the most ancient objects that can be observed optically (infrared)?


texts: How does Io's atmosphere behave locally near volcanic plumes?

texts:
Io's surface air pressure is about $0.3 {\rm mPa}$ but Io's atmosphere is strongly variable, depending on whether it's on the near side or far side of Io (relative to Jupiter) and it collapses at night. When it's heated up, it rises again, and so it also gets thicker in Io's volcanic plumes.
I'd like to know just what does happen with the atmosphere above a volcanic crater during an eruption? How much thicker does it get?
The eruption temperatures reach ${\rm 1\,300^\circ C} \, (2 \,400 {\rm F} )$.


texts: Does the gravity oppose to the Universe expansion?

texts:
I'm trying to understanding the very basic of the current cosmology.
I searched in the old questions but I found nothing that answers specifically to my questions.

As far as I understand, we have to think the "expansion" more like a "streching" of the space that makes room for "new" space. This is confirmed because the Universe is homogeneous and non-local.

First question: does the gravity contrast this expansion? In other words: does the space expand more in the areas with less gravity (i.e. among galaxies) and less in the nearby of stars and planets?

If we imagine to place a ruler between two stars, say at 10 ly, it would "extend" over time - even if we will still read 10 ly, right? But if now we place another ruler that was kept in our (huge) pocket, it will measure a longer distance. Is it correct?

That because the first ruler has expanded together the space between the stars, while the second one endured the force of gravity and was kept rolled up so it wasn't able to expand.


texts: What fills the new space created during expansion?

texts: Does it remain void and pushes even more or will virtual particles eventually create normal matter?


texts: Can I see "my own hand" in the void space?

texts: If I were floating in a void (far away from any galaxy or cluster), would the light from these objects at such distances be enough to see for example, my hand?


texts: What particles does a black hole emit when it evaporates itself?

texts:
Due to Hawking Radiation, after a very long time, a black hole will eventually disappear.

But where does this "evaporation" go? What is this made of?


texts:
I'm looking for any exoplanet nomenclature, official, semi-official, proposed, or just a good idea, beyond what can already be found on Wikipedia at

http://en.wikipedia.org/wiki/Exoplanet#Other_naming_systems

Or via the obvious Google searches.

This is a vaguely sci-fi related request.  Lowercase Latin alphabet isn't going to do it once we get out there, and I like the proposal for Greece-roman mythology but there are simply too many planets now, and will be more over time.

As a side issue I'm already familiar with Ian Banks Culture addressing nomenclature, so I accept that humanity being what it is, we can expect about a hundred or so "Vulcan" orbiting various different stars, much as there are 37 "Greenville"s in the USA, currently.

A pointer to a really great fictional idea or naming scheme aside from the schemes mentioned about might be useful.

Interesting technical (non literary) naming schemes beyond the most obvious and trivial ordinal systems could be interesting.


texts: What are the arguments against the Feng and Gallo thin disk explanation of galactic rotation curves?

texts:
The well-known galaxy rotation problem is described here. Basically (as one moves outward from the galactic centre, $R$ increasing) the observed pattern of variation in orbital speed $V$ is very different from the pattern expected on the basis of the distribution of mass inferred from detectable radiation. This is illustrated by the two curves in the following figure.

Feng and Gallo in several papers such as this 2010 article have proposed a method for modelling mass distributions in discoidal galaxies.  The method can be applied to an individual galaxy to produce a "tailor-made" mass distribution which (by applying basic Newtonian physics) predicts a galactic rotation curve matching the curve observed for the galaxy. They explain the failure of other attempts, using "ordinary" physics, to predict observed galactic rotations on the use of crude luminosity:mass assumptions and on the inappropriate application of Keplerian models to galaxies.

"Mysterious" explanations of the galaxy rotation problem such as Dark Matter  and MOND are still being considered seriously. Presumably therefore Feng and Gallo's ideas are not widely accepted.  What are the reasons for the rejection of their explanations?